With the diversification of the cleaning manners, a robot vacuum cleaner appears in more and more families. The operation manner of the robot vacuum cleaner is mainly divided into “suction” and “sweep”. Similar to a traditional vacuum cleaner, the “suction” of the robot vacuum cleaner cannot do without a fan, and a structure of the fan is closely related to magnitude of a “suction force”. Generally, the fan type applied in the robot vacuum cleaner includes an axial fan A as illustrated in FIG. 1. The axial fan A throws air to the periphery by an electric motor C that drives a rotor impeller B to rotate, thereby generating the suction force. The fan type in the robot vacuum cleaner also includes a centrifugal fan D as illustrated in FIG. 2. An air duct structure of the centrifugal fan D is similar to a volute, and the stator impeller is driven to rotate by the motor at a center of the centrifugal fan D, thereby generating the suction force. In the above fans, the air duct is mainly formed and defined by a housing of the fan, and the air duct has a poor air outlet guiding performance, this results in a relatively small suction force of the fan, such that the robot vacuum cleaner has a poor cleaning effect and a low efficiency.